The Government has rights in this invention pursuant to Contract No. N00024-85-C-5500, awarded by the U.S. Navy.
In the electronics industry it is common to construct circuit boards by placing the electronic components on the board in the proper position with respect to the printed circuitry and then to form all the soldered connections simultaneously by use of an apparatus such as a wave soldering device. There are however, several problems associated with this procedure.
It is important that all connections to be soldered be properly fluxed before entering the wave soldering device, so that adequate solder connections will be made. Many of the techniques now available do not allow for rapid and complete flux application.
It is also important that the printed circuitry on the board and the contacts on the various components be clean, so that both the flux and the solder can properly adhere. Again, the techniques currently available do not provide for rapid and complete cleaning. In fact, in many cases, the cleaning fluids fail to reach all areas of the board or the components or they fail to adequately remove the contaminants that are trapped in small openings.
In addition, following the soldering step it is often necessary to clean the boards again to remove excess flux or solder and to be sure that through holes in the board which are intended to be left open are cleaned of any solder or flux that may have closed them.
In the past there have been numerous devices to spray fluids on passing articles. Commonly, the articles are transported through a spray chamber on a moving belt or similar device and are sprayed with fluid as they pass spray nozzles. Such devices have been used in the past to wash such diverse things as vegetables and paper making felts, to apply etching solutions to metal plates or to apply solder to electrical conductors on circuit boards. In most cases the impact of the sprays on the articles being washed, etched, soldered, etc., has not had any significant effect on the structure of the article itself or on its travel through the spray chamber. Unwanted movement of light objects such as cans on a conveyer belt under the force of the cleaning spray has been compensated for simply by having a second conveyer belt placed in direct proximity to the cans to limit any such motion.
Circuit card assemblies pose a much more difficult problem, however. The various components are placed on the board but are not secured firmly in their positions until the soldering step has been completed. Consequently, the cleaning and fluxing steps before the soldering must be done with considerable care so that the components are not dislodged from the proper positions. Many of the cleaning devices heretofore known have been unable to properly clean or flux such circuit card assemblies without causing significant amounts of dislodging and dislocation of the components.
It would therefore be of considerable interest to have a device which could readily clean and flux circuit card assemblies without risk of dislocating or dislodging any of the components. It would also be of interest to have such a device which could effectively clean and flux the circuit card assemblies by insuring that the cleaning or fluxing fluids would penetrate into all parts of the assembly, thoroughly remove contaminants and apply flux to the appropriate contacts. It would also be advantageous for such a device to be capable of being used following the soldering of the circuit card assemblies to remove excess flux and solder and to insure that all through passages were properly opened.